1. Field of the Invention
This invention is concerned with radiation detection means of the gas-filled counter tube type. Specifically, the invention relates to a means for reducing or eliminating count rate drift of radiation detection means caused by the accumulation of electrical charge on insulating surfaces contained therein. More particularly, the invention is concerned with the application of an electrically conductive coating to the interior insulating surfaces of said radiation detection means to reduce or eliminate accumulated charge thereon and thereby reduce count rate drift.
2. Description of the Prior Art
Radiation detectors of the gas-filled counter tube type are well-known and include ionization chambers, proportional counters, and Geiger-Mueller counters as typically shown in Boyd et al U.S. Pat. No. 3,043,954 and Goodings et al U.S. Pat. No. 3,702,409.
Generally speaking, gas-filled counter tube type radiation detectors consist of a conducting cylinder and an axially mounted wire anode between which a potential difference is maintained.
Ionization within the conducting cylinder occurs when a particle or ray of sufficient energy strikes an atom of gas in the conducting cylinder and causes the atom to eject an electron. As a result, the atom acquires a positive charge since it has lost an electron. In the presence of a potential difference, recombination will be largely prevented by the respective drift of positive and negative ions towards the electrodes carrying opposite polarity. This, in effect, changes the charge on the electrode system and the change in potential so produced provides an electrical indication of the ionizing event.
A problem encountered in the use of these types of radiation counter tubes is a drift in the count rate of the tube with time. This drift can occur even when the tube is exposed to a constant flux and may result in an output change of as much as several percent of the total number of counts. The cause of the drift in count rate is an accumulation of electrical charge on insulating surfaces within the conducting cylinder. There is, therefore, a need for a radiation detector of the gas-filled counter tube type which avoids accumulation of electrical charge on the insulating surfaces therein and can hence reduce or eliminate count rate drift. The present invention represents an improvement over the prior art in that it allows accurate and reliable count rate measurements to be made with gas-filled counter tubes.